The present invention relates to fluid loss control and, more particularly, to using fluid loss control additives that comprise a water-soluble polymer having hydrophobic or hydrophilic modification.
A problem often encountered during subterranean treatments is the undesired loss or leak off of fluid into the formation. This undesired loss or leak off is commonly referred to as “fluid loss.” Fluid loss can occur in drilling operations, cleanup operations, workover operations, completion operations, stimulation treatments (e.g., fracturing, acidizing), and sand control treatments (e.g., gravel packing). In fracturing treatments, fluid loss into the formation may result in a reduction in fluid efficiency, such that the fracturing fluid cannot propagate the fracture as desired. As used herein, the term “treatment,” or “treating,” refers to any subterranean treatment that uses a fluid in conjunction with a desired function and/or for a desired purpose. The term “treatment,” or “treating,” does not imply any particular action by the fluid or any particular component thereof.
Fluid loss into the formation may result from a number of downhole conditions, such as high-formation permeability, overbalance pressures, perforated or open-hole intervals in the well bore, and large differential pressures associated with differential segregation in wells completed in a multilayer reservoir. In some instances, the fluid loss may be into a low-pressure portion of the formation due to overbalance pressures, for example, where a well is completed in a multilayer reservoir.
Traditional methods of combating fluid loss may involve mechanical or chemical isolation of the portions of the subterranean formation into which fluid loss occurs. However, in certain subterranean treatments (e.g., workover operations), the mechanical completion itself may not allow for such isolation to occur. In some instances, the use of low-density fluids, such as hydrocarbon-based fluids or foamed fluids, may be used to combat fluid loss into the formation. However, in some instances, well conditions may not allow for the use of hydrocarbon-based fluids, for instance, due to the hydrostatic pressures associated with the hydrocarbon-based fluids. Furthermore, the use of foamed fluids may add undesired expense and complexity to the well bore cleanup operation, as well as additional safety considerations.
In other instances, to prevent fluid loss from occurring, fluid loss control additives commonly may be included in the treatment fluids. Examples of commonly used fluid loss control additives include, but are not limited to, gelling agents, such as hydroxyethylcellulose and xanthan. Additional fluid loss control may be provided by crosslinking the gelling agent or by including fluid loss control materials, such as sized solids (e.g., calcium carbonate), silica particles, oil-soluble resins, and degradable particles, in the treatment fluids. The fluid loss control materials may be used in combination with or separately from the conventional fluid loss control additives. These conventional methods commonly work at the well bore and/or formation face and if they invade the reservoir, formation damage may occur. Additionally, the use of crosslinked fluids may impact fracture geometry, for example, creating wider, shorter fractures. Further, the crosslinked fluids may form a filter cake, which may be detrimental to the production of reservoir fluids.
Chemical fluid loss control pills also may be used to combat fluid loss. Conventional chemical fluid loss control pills may be characterized as either solids-containing pills or solids-free pills. Examples of solids-containing pills include sized-salt pills and sized-carbonate pills. These solids-containing pills often are not optimized for the particular downhole hardware and conditions that may be encountered. For instance, the particle sizes of the solids may not be optimized for a particular application and, as a result, may increase the risk of invasion into the interior of the formation matrix, which may greatly increase the difficulty of removal by subsequent remedial treatments. Additionally, high-solids loading in the pills, in conjunction with the large volumes of these pills needed to control fluid losses, may greatly increase the complexity of subsequent cleanup. Furthermore, high loading of starches and biopolymers in the sized salt pills may add to the difficulty of cleanup either by flow back or remedial treatments. Solids-free fluid loss control pills commonly comprise hydrated polymer gels that may not be effective without some invasion into the formation matrix. These pills typically require large volumes to control fluid loss and remedial treatments to remove.
Once fluid loss control is no longer required, for example, after completing a treatment, remedial treatments may be required to remove the previously placed pills, for example, so that the wells may be placed into production. For example, a chemical breaker, such as an acid, oxidizer, or enzyme may be used to either dissolve the solids or reduce the viscosity of the pill. In many instances, however, use of a chemical breaker to remove the pill from inside the well bore and/or the formation matrix may be either ineffective or not a viable economic option. For example, due to production equipment in the well bore, uniform placement of the breaker into the portion of the formation treated with the pill may not be possible. Furthermore, the chemical breakers may be corrosive to downhole tools. Additionally, as the chemical breakers leak off into the formation, they may carry undissolved fines that may plug and/or damage the formation or may produce undesirable reactions with the formation.